Method for transmitting a buffer status report in a communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for transmitting, by a user equipment (UE), a buffer status report (BSR) in a wireless communication system, the method comprising: triggering, by a medium access control (MAC) entity, a buffer status report (BSR); and transmitting the buffer status report, wherein the buffer status report includes a packet data convergence protocol (PDCP) buffer size for a radio bearer only if PDCP BSR condition is met.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119(e), this application claims the benefit of U.S. Provisional Patent Application No. 62/371,191, filed on Aug. 4, 2016, the contents of which are hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system and, more particularly, to a method for transmitting a buffer status report (BSR) in a communication system and a device therefor.

Discussion of the Related Art

As an example of a mobile communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (hereinafter, referred to as LTE) communication system is described in brief.

FIG. 1 is a view schematically illustrating a network structure of an E-UMTS as an exemplary radio communication system. An Evolved Universal Mobile Telecommunications System (E-UMTS) is an advanced version of a conventional Universal Mobile Telecommunications System (UMTS) and basic standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, reference can be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located at an end of the network (E-UTRAN) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink (DL) or uplink (UL) transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths. The eNB controls data transmission or reception to and from a plurality of UEs. The eNB transmits DL scheduling information of DL data to a corresponding UE so as to inform the UE of a time/frequency domain in which the DL data is supposed to be transmitted, coding, a data size, and hybrid automatic repeat and request (HARQ)-related information. In addition, the eNB transmits UL scheduling information of UL data to a corresponding UE so as to inform the UE of a time/frequency domain which may be used by the UE, coding, a data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include the AG and a network node or the like for user registration of UEs. The AG manages the mobility of a UE on a tracking area (TA) basis. One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTE based on wideband code division multiple access (WCDMA), the demands and expectations of users and service providers are on the rise. In addition, considering other radio access technologies under development, new technological evolution is required to secure high competitiveness in the future. Decrease in cost per bit, increase in service availability, flexible use of frequency bands, a simplified structure, an open interface, appropriate power consumption of UEs, and the like are required.

SUMMARY OF THE INVENTION

The object of the present invention can be achieved by providing a method for transmitting, by a user equipment (UE), a buffer status report (BSR) in a wireless communication system, the method comprising: triggering, by a medium access control (MAC) entity, a buffer status report (BSR); and transmitting the buffer status report, wherein the buffer status report includes a packet data convergence protocol (PDCP) buffer size for a radio bearer only if PDCP BSR condition is met.

In another aspect of the present invention provided herein is an UE operating in wireless communication system, the UE comprising: a radio frequency (RF) module configured to transmit/receive signals to/from a network; and a processor configured to process the signals, wherein the processor is configured to: trigger, by a medium access control (MAC) entity, a buffer status report (BSR); and transmit the buffer status report, wherein the buffer status report includes a packet data convergence protocol (PDCP) buffer size for a radio bearer only if PDCP BSR condition is met.

Preferably, the buffer status report includes a first value for the PDCP buffer size if the PDCP BSR condition is met and a second value for a radio link control (RLC) buffer size.

Preferably, the MAC entity is a MAC entity configured to transmit the PDCP buffer size.

Preferably, the PDCP BSR condition is at least one of: when the PDCP buffer size is equal to or larger than a threshold, when a certain number of BSRs without the PDCP buffer size is generated by the MAC entity, or when a certain time has passed since a last BSR without PDCP buffer size is generated by the MAC entity.

Preferably, the radio bearer comprises one PDCP entity and multiple RLC entities.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention.

FIG. 1 is a diagram showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a wireless communication system;

FIG. 2A is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS), and FIG. 2B is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3rd generation partnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in an E-UMTS system;

FIG. 5 is a diagram for a general overview of the LTE protocol architecture for the downlink.

FIG. 6 is a diagram for MAC header and SDU (Service Data Unit) multiplexing.

FIG. 7 is a diagram for signaling of buffer status and power-headroom reports.

FIG. 8 is a diagram for short BSR MAC CE.

FIG. 9 is a diagram for long BSR MAC CE.

FIG. 10 is an exemplary diagram illustrating legacy BSR operation in multiple connectivity.

FIG. 11 is a flowchart according to an embodiment of the present invention.

FIG. 12 is a block diagram of a communication apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Universal mobile telecommunications system (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3G LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Hereinafter, structures, operations, and other features of the present invention will be readily understood from the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Embodiments described later are examples in which technical features of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using a long term evolution (LTE) system and a LTE-advanced (LTE-A) system in the present specification, they are purely exemplary. Therefore, the embodiments of the present invention are applicable to any other communication system corresponding to the above definition. In addition, although the embodiments of the present invention are described based on a frequency division duplex (FDD) scheme in the present specification, the embodiments of the present invention may be easily modified and applied to a half-duplex FDD (H-FDD) scheme or a time division duplex (TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolved universal mobile telecommunication system (E-UMTS). The E-UMTS may be also referred to as an LTE system. The communication network is widely deployed to provide a variety of communication services such as voice (VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTS terrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC) and one or more user equipment. The E-UTRAN may include one or more evolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 may be located in one cell. One or more E-UTRAN mobility management entity (MME)/system architecture evolution (SAE) gateways 30 may be positioned at the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE 10, and “uplink” refers to communication from the UE to an eNodeB. UE 10 refers to communication equipment carried by a user and may be also referred to as a mobile station (MS), a user terminal (UT), a subscriber station (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRAN and a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a user plane and a control plane to the UE 10. MME/SAE gateway 30 provides an end point of a session and mobility management function for UE 10. The eNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE 10, and may also be referred to as a base station (BS) or an access point. One eNodeB 20 may be deployed per cell. An interface for transmitting user traffic or control traffic may be used between eNodeBs 20.

The MME provides various functions including NAS signaling to eNodeBs 20, NAS signaling security, AS Security control, Inter CN node signaling for mobility between 3GPP access networks, Idle mode UE Reachability (including control and execution of paging retransmission), Tracking Area list management (for UE in idle and active mode), PDN GW and Serving GW selection, MME selection for handovers with MME change, SGSN selection for handovers to 2G or 3G 3GPP access networks, Roaming, Authentication, Bearer management functions including dedicated bearer establishment, Support for PWS (which includes ETWS and CMAS) message transmission. The SAE gateway host provides assorted functions including Per-user based packet filtering (by e.g. deep packet inspection), Lawful Interception, UE IP address allocation, Transport level packet marking in the downlink, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAE gateway 30 will be referred to herein simply as a “gateway,” but it is understood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30 via the S1 interface. The eNodeBs 20 may be connected to each other via an X2 interface and neighboring eNodeBs may have a meshed network structure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway 30, routing toward the gateway during a Radio Resource Control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of Broadcast Channel (BCCH) information, dynamic allocation of resources to UEs 10 in both uplink and downlink, configuration and provisioning of eNodeB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE ACTIVE state. In the EPC, and as noted above, gateway 30 may perform functions of paging origination, LTE-IDLE state management, ciphering of the user plane, System Architecture Evolution (SAE) bearer control, and ciphering and integrity protection of Non-Access Stratum (NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway (S-GW), and a packet data network-gateway (PDN-GW). The MME has information about connections and capabilities of UEs, mainly for use in managing the mobility of the UEs. The S-GW is a gateway having the E-UTRAN as an end point, and the PDN-GW is a gateway having a packet data network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radio interface protocol between a UE and an E-UTRAN based on a 3GPP radio access network standard. The control plane refers to a path used for transmitting control messages used for managing a call between the UE and the E-UTRAN. The user plane refers to a path used for transmitting data generated in an application layer, e.g., voice data or Internet packet data.

A physical (PHY) layer of a first layer provides an information transfer service to a higher layer using a physical channel. The PHY layer is connected to a medium access control (MAC) layer located on the higher layer via a transport channel. Data is transported between the MAC layer and the PHY layer via the transport channel. Data is transported between a physical layer of a transmitting side and a physical layer of a receiving side via physical channels. The physical channels use time and frequency as radio resources. In detail, the physical channel is modulated using an orthogonal frequency division multiple access (OFDMA) scheme in downlink and is modulated using a single carrier frequency division multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio link control (RLC) layer of a higher layer via a logical channel. The RLC layer of the second layer supports reliable data transmission. A function of the RLC layer may be implemented by a functional block of the MAC layer. A packet data convergence protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission of an Internet protocol (IP) packet such as an IP version 4 (IPv4) packet or an IP version 6 (IPv6) packet in a radio interface having a relatively small bandwidth.

A radio resource control (RRC) layer located at the bottom of a third layer is defined only in the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to configuration, re-configuration, and release of radio bearers (RBs). An RB refers to a service that the second layer provides for data transmission between the UE and the E-UTRAN. To this end, the RRC layer of the UE and the RRC layer of the E-UTRAN exchange RRC messages with each other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplink transmission service to a plurality of UEs in the bandwidth. Different cells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN to the UE include a broadcast channel (BCH) for transmission of system information, a paging channel (PCH) for transmission of paging messages, and a downlink shared channel (SCH) for transmission of user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through the downlink SCH and may also be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to the E-UTRAN include a random access channel (RACH) for transmission of initial control messages and an uplink SCH for transmission of user traffic or control messages. Logical channels that are defined above the transport channels and mapped to the transport channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure used in an E-UMTS system. A physical channel includes several subframes on a time axis and several subcarriers on a frequency axis. Here, one subframe includes a plurality of symbols on the time axis. One subframe includes a plurality of resource blocks and one resource block includes a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use certain subcarriers of certain symbols (e.g., a first symbol) of a subframe for a physical downlink control channel (PDCCH), that is, an L1/L2 control channel. In FIG. 4, an L1/L2 control information transmission area (PDCCH) and a data area (PDSCH) are shown. In one embodiment, a radio frame of 10 ms is used and one radio frame includes 10 subframes. In addition, one subframe includes two consecutive slots. The length of one slot may be 0.5 ms. In addition, one subframe includes a plurality of OFDM symbols and a portion (e.g., a first symbol) of the plurality of OFDM symbols may be used for transmitting the L1/L2 control information. A transmission time interval (TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, which is a physical channel, using a DL-SCH which is a transmission channel, except a certain control signal or certain service data. Information indicating to which UE (one or a plurality of UEs) PDSCH data is transmitted and how the UE receive and decode PDSCH data is transmitted in a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with a radio network temporary identity (RNTI) “A” and information about data is transmitted using a radio resource “B” (e.g., a frequency location) and transmission format information “C” (e.g., a transmission block size, modulation, coding information or the like) via a certain subframe. Then, one or more UEs located in a cell monitor the PDCCH using its RNTI information. And, a specific UE with RNTI “A” reads the PDCCH and then receive the PDSCH indicated by B and C in the PDCCH information.

FIG. 5 is a diagram for a general overview of the LTE protocol architecture for the downlink.

A general overview of the LTE protocol architecture for the downlink is illustrated in FIG. 5. Furthermore, the LTE protocol structure related to uplink transmissions is similar to the downlink structure in FIG. 5, although there are differences with respect to transport format selection and multi-antenna transmission.

Data to be transmitted in the downlink enters in the form of IP packets on one of the SAE bearers (501). Prior to transmission over the radio interface, incoming IP packets are passed through multiple protocol entities, summarized below and described in more detail in the following sections:

-   -   Packet Data Convergence Protocol (PDCP, 503) performs IP header         compression to reduce the number of bits necessary to transmit         over the radio interface. The header-compression mechanism is         based on ROHC, a standardized header-compression algorithm used         in WCDMA as well as several other mobile-communication         standards. PDCP (503) is also responsible for ciphering and         integrity protection of the transmitted data. At the receiver         side, the PDCP protocol performs the corresponding deciphering         and decompression operations. There is one PDCP entity per radio         bearer configured for a mobile terminal.     -   Radio Link Control (RLC, 505) is responsible for         segmentation/concatenation, retransmission handling, and         in-sequence delivery to higher layers. Unlike WCDMA, the RLC         protocol is located in the eNodeB since there is only a single         type of node in the LTE radio-access-network architecture. The         RLC (505) offers services to the PDCP (503) in the form of radio         bearers. There is one RLC entity per radio bearer configured for         a terminal.

There is one RLC entity per logical channel configured for a terminal, where each RLC entity is responsible for: i) segmentation, concatenation, and reassembly of RLC SDUs; ii) RLC retransmission; and iii) in-sequence delivery and duplicate detection for the corresponding logical channel.

Other noteworthy features of the RLC are: (1) the handling of varying PDU sizes; and (2) the possibility for close interaction between the hybrid-ARQ and RLC protocols. Finally, the fact that there is one RLC entity per logical channel and one hybrid-ARQ entity per component carrier implies that one RLC entity may interact with multiple hybrid-ARQ entities in the case of carrier aggregation.

The purpose of the segmentation and concatenation mechanism is to generate RLC PDUs of appropriate size from the incoming RLC SDUs. One possibility would be to define a fixed PDU size, a size that would result in a compromise. If the size were too large, it would not be possible to support the lowest data rates. Also, excessive padding would be required in some scenarios. A single small PDU size, however, would result in a high overhead from the header included with each PDU. To avoid these drawbacks, which is especially important given the very large dynamic range of data rates supported by LTE, the RLC PDU size varies dynamically.

In process of segmentation and concatenation of RLC SDUs into RLC PDUs, a header includes, among other fields, a sequence number, which is used by the reordering and retransmission mechanisms. The reassembly function at the receiver side performs the reverse operation to reassemble the SDUs from the received PDUs.

-   -   Medium Access Control (MAC, 507) handles hybrid-ARQ         retransmissions and uplink and downlink scheduling. The         scheduling functionality is located in the eNodeB, which has one         MAC entity per cell, for both uplink and downlink. The         hybrid-ARQ protocol part is present in both the transmitting and         receiving end of the MAC protocol. The MAC (507) offers services         to the RLC (505) in the form of logical channels (509).     -   Physical Layer (PHY, 511), handles coding/decoding,         modulation/demodulation, multi-antenna mapping, and other         typical physical layer functions. The physical layer (511)         offers services to the MAC layer (507) in the form of transport         channels (513).

The Logical Channel Prioritization procedure is applied when a new transmission is performed.

RRC controls the scheduling of uplink data by signalling for each logical channel: priority where an increasing priority value indicates a lower priority level, prioritisedBitRate which sets the Prioritized Bit Rate (PBR), bucketSizeDuration which sets the Bucket Size Duration (BSD).

The MAC entity shall maintain a variable Bj for each logical channel j. Bj shall be initialized to zero when the related logical channel is established, and incremented by the product PBR×TTI duration for each TTI, where PBR is Prioritized Bit Rate of logical channel j. However, the value of Bj can never exceed the bucket size and if the value of Bj is larger than the bucket size of logical channel j, it shall be set to the bucket size. The bucket size of a logical channel is equal to PBR×BSD, where PBR and BSD are configured by upper layers.

The MAC entity shall perform the following Logical Channel Prioritization procedure when a new transmission is performed. The MAC entity shall allocate resources to the logical channels in the following steps.

Step 1: All the logical channels with Bj>0 are allocated resources in a decreasing priority order. If the PBR of a logical channel is set to “infinity”, the MAC entity shall allocate resources for all the data that is available for transmission on the logical channel before meeting the PBR of the lower priority logical channels.

Step 2: the MAC entity shall decrement Bj by the total size of MAC SDUs served to logical channel j in Step 1.

Step 3: if any resources remain, all the logical channels are served in a strict decreasing priority order (regardless of the value of Bj) until either the data for that logical channel or the UL grant is exhausted, whichever comes first. Logical channels configured with equal priority should be served equally.

The UE shall also follow the rules below during the scheduling procedures above.

-   -   The UE should not segment an RLC SDU (or partially transmitted         SDU or retransmitted RLC PDU) if the whole SDU (or partially         transmitted SDU or retransmitted RLC PDU) fits into the         remaining resources of the associated MAC entity.     -   If the UE segments an RLC SDU from the logical channel, it shall         maximize the size of the segment to fill the grant of the         associated MAC entity as much as possible.     -   The UE should maximize the transmission of data.     -   if the MAC entity is given an UL grant size that is equal to or         larger than 4 bytes while having data available for         transmission, the MAC entity shall not transmit only padding BSR         and/or padding (unless the UL grant size is less than 7 bytes         and an AMD PDU segment needs to be transmitted).

The MAC entity shall not transmit data for a logical channel corresponding to a radio bearer that is suspended.

For the Logical Channel Prioritization procedure, the MAC entity shall take into account the following relative priority in decreasing order.

-   -   MAC control element for C-RNTI or data from UL-CCCH;     -   MAC control element for BSR, with exception of BSR included for         padding;     -   MAC control element for PHR, Extended PHR, or Dual Connectivity         PHR;     -   MAC control element for Sidelink BSR, with exception of Sidelink         BSR included for padding;     -   data from any Logical Channel, except data from UL-CCCH;     -   MAC control element for BSR included for padding;     -   MAC control element for Sidelink BSR included for padding.

When the MAC entity is requested to transmit multiple MAC PDUs in one TTI, steps 1 to 3 and the associated rules may be applied either to each grant independently or to the sum of the capacities of the grants. Also the order in which the grants are processed is left up to UE implementation. It is up to the UE implementation to decide in which MAC PDU a MAC control element is included when MAC entity is requested to transmit multiple MAC PDUs in one TTI. When the UE is requested to generate MAC PDU(s) in two MAC entities in one TTI, it is up to UE implementation in which order the grants are processed.

The Buffer Status Reporting (BSR) procedure is used to provide a serving eNB with information about the amount of data available for transmission in the UL buffers of the UE. RRC may control BSR reporting by configuring the two timers periodicBSR-Timer and retxBSR-Timer and by, for each logical channel, optionally signaling Logical Channel Group which allocates the logical channel to an LCG (Logical Channel Group).

For the Buffer Status reporting procedure, the UE may consider all radio bearers which are not suspended and may consider radio bearers which are suspended. A Buffer Status Report (BSR) may be triggered if any of the following events occur:

-   -   UL data, for a logical channel which belongs to a LCG, becomes         available for transmission in the RLC entity or in the PDCP         entity and either the data belongs to a logical channel with         higher priority than the priorities of the logical channels         which belong to any LCG and for which data is already available         for transmission, or there is no data available for transmission         for any of the logical channels which belong to a LCG, in which         case the BSR is referred below to as “Regular BSR”;     -   UL resources are allocated and number of padding bits is equal         to or larger than the size of the Buffer Status Report MAC         control element plus its subheader, in which case the BSR is         referred below to as “Padding BSR”;     -   retxBSR-Timer expires and the UE has data available for         transmission for any of the logical channels which belong to a         LCG, in which case the BSR is referred below to as “Regular         BSR”;     -   periodicBSR-Timer expires, in which case the BSR is referred         below to as “Periodic BSR”.

For Regular and Periodic BSR, if more than one LCG has data available for transmission in the TTI where the BSR is transmitted, the UE may report Long BSR. If else, the UE may report Short BSR.

If the Buffer Status reporting procedure determines that at least one BSR has been triggered and not cancelled, if the UE has UL resources allocated for new transmission for this TTI, the UE may instruct the Multiplexing and Assembly procedure to generate the BSR MAC control element(s), start or restart periodicBSR-Timer except when all the generated BSRs are Truncated BSRs, and start or restart retxBSR-Timer.

Else if a Regular BSR has been triggered, if an uplink grant is not configured or the Regular BSR was not triggered due to data becoming available for transmission for a logical channel for which logical channel SR masking (logicalChannelSR-Mask) is setup by upper layers, a Scheduling Request shall be triggered.

A MAC PDU may contain at most one MAC BSR control element, even when multiple events trigger a BSR by the time a BSR can be transmitted in which case the Regular BSR and the Periodic BSR shall have precedence over the padding BSR.

The UE may restart retxBSR-Timer upon indication of a grant for transmission of new data on any UL-SCH.

All triggered BSRs may be cancelled in case UL grants in this subframe can accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its subheader. All triggered BSRs shall be cancelled when a BSR is included in a MAC PDU for transmission.

The UE shall transmit at most one Regular/Periodic BSR in a TTI. If the UE is requested to transmit multiple MAC PDUs in a TTI, it may include a padding BSR in any of the MAC PDUs which do not contain a Regular/Periodic BSR.

All BSRs transmitted in a TTI always reflect the buffer status after all MAC PDUs have been built for this TTI. Each LCG shall report at the most one buffer status value per TTI and this value shall be reported in all BSRs reporting buffer status for this LCG.

In summary, the BSR is triggered in any of the following situation:

i) when data arrive for a logical channel which has higher priority than the logical channels whose buffers are not empty;

ii) when data become available for the UE's buffer, which is empty;

iii) when the retxBSR-Timer expires and there is still data in the UE's buffer;

iv) when a periodicBSR-Timer expires; or

v) when the remaining space in a MAC PDU can accommodate a BSR.

The sidelink Buffer Status reporting procedure is used to provide the serving eNB with information about the amount of sidelink data available for transmission in the SL buffers associated with the MAC entity. RRC controls BSR reporting for the sidelink by configuring the two timers periodic-BSR-TimerSL and retx-BSR-TimerSL. Each sidelink logical channel belongs to a ProSe Destination. Each sidelink logical channel is allocated to an LCG depending on the priority of the sidelink logical channel and the mapping between LCG ID and priority which is provided by upper layers in logicalChGroupInfoList. LCG is defined per ProSe Destination.

A sidelink Buffer Status Report (BSR) shall be triggered if any of the following events occur: if the MAC entity has a configured SL-RNTI i) SL data, for a sidelink logical channel of a ProSe Destination, becomes available for transmission in the RLC entity or in the PDCP entity and either the data belongs to a sidelink logical channel with higher priority than the priorities of the sidelink logical channels which belong to any LCG belonging to the same ProSe Destination and for which data is already available for transmission, or there is currently no data available for transmission for any of the sidelink logical channels belonging to the same ProSe Destination, in which case the Sidelink BSR is referred below to as “Regular Sidelink BSR”, ii) UL resources are allocated and number of padding bits remaining after a Padding BSR has been triggered is equal to or larger than the size of the Sidelink BSR MAC control element containing the buffer status for at least one LCG of a ProSe Destination plus its subheader, in which case the Sidelink BSR is referred below to as “Padding Sidelink BSR”, iii) retx-BSR-TimerSL expires and the MAC entity has data available for transmission for any of the sidelink logical channels, in which case the Sidelink BSR is referred below to as “Regular Sidelink BSR”, iv) periodic-BSR-TimerSL expires, in which case the Sidelink BSR is referred below to as “Periodic Sidelink BSR”. Else, An SL-RNTI is configured by upper layers and SL data is available for transmission in the RLC entity or in the PDCP entity, in which case the Sidelink BSR is referred below to as “Regular Sidelink BSR”.

For Regular and Periodic Sidelink BSR, if the number of bits in the UL grant is equal to or larger than the size of a Sidelink BSR containing buffer status for all LCGs having data available for transmission plus its subheader, the MAC entity reports Sidelink BSR containing buffer status for all LCGs having data available for transmission. Else, the MAC entity reports Truncated Sidelink BSR containing buffer status for as many LCGs having data available for transmission as possible, taking the number of bits in the UL grant into consideration.

If the Buffer Status reporting procedure determines that at least one Sidelink BSR has been triggered and not cancelled: if the MAC entity has UL resources allocated for new transmission for this TTI and the allocated UL resources can accommodate a Sidelink BSR MAC control element plus its subheader as a result of logical channel prioritization, the MAC entity instructs the Multiplexing and Assembly procedure to generate the Sidelink BSR MAC control element(s), starts or restarts periodic-BSR-TimerSL except when all the generated Sidelink BSRs are Truncated Sidelink BSRs, and starts or restarts retx-BSR-TimerSL. Else if a Regular Sidelink BSR has been triggered, if an uplink grant is not configured, a Scheduling Request shall be triggered.

A MAC PDU shall contain at most one Sidelink BSR MAC control element, even when multiple events trigger a Sidelink BSR by the time a Sidelink BSR can be transmitted in which case the Regular Sidelink BSR and the Periodic Sidelink BSR shall have precedence over the padding Sidelink BSR.

The MAC entity shall restart retx-BSR-TimerSL upon reception of an SL grant.

All triggered regular Sidelink BSRs shall be cancelled in case the remaining configured SL grant(s) valid for this SC Period can accommodate all pending data available for transmission. All triggered Sidelink BSRs shall be cancelled in case the MAC entity has no data available for transmission for any of the sidelink logical channels. All triggered Sidelink BSRs shall be cancelled when a Sidelink BSR (except for Truncated Sidelink BSR) is included in a MAC PDU for transmission. All triggered Sidelink BSRs shall be cancelled, and retx-BSR-TimerSL and periodic-BSR-TimerSL shall be stopped, when upper layers configure autonomous resource selection.

The MAC entity shall transmit at most one Regular/Periodic Sidelink BSR in a TTI. If the MAC entity is requested to transmit multiple MAC PDUs in a TTI, it may include a padding Sidelink BSR in any of the MAC PDUs which do not contain a Regular/Periodic Sidelink BSR.

All Sidelink BSRs transmitted in a TTI always reflect the buffer status after all MAC PDUs have been built for this TTI. Each LCG shall report at the most one buffer status value per TTI and this value shall be reported in all Sidelink BSRs reporting buffer status for this LCG.

FIG. 6 is a diagram for MAC header and SDU (Service Data Unit) multiplexing.

The MAC layer handles logical-channel multiplexing, hybrid-ARQ retransmissions, and uplink and downlink scheduling. It is also responsible for multiplexing/demultiplexing data across multiple component carriers when carrier aggregation is used.

To support priority handling, multiple logical channels, where each logical channel has its own RLC entity, can be multiplexed into one transport channel by the MAC layer. At the receiver, the MAC layer handles the corresponding demultiplexing and forwards the RLC PDUs to their respective RLC entity for in-sequence delivery and the other functions handled by the RLC. To support the demultiplexing at the receiver, a MAC header, shown in FIG. 6, is used. To each RLC PDU, there is an associated sub-header in the MAC header. The sub-header contains the identity of the logical channel (LCID) from which the RLC PDU originated and the length of the PDU in bytes. There is also a flag indicating whether this is the last sub-header or not. One or several RLC PDUs, together with the MAC header and, if necessary, padding to meet the scheduled transport-block size, form one transport block which is forwarded to the physical layer.

In addition to multiplexing of different logical channels, the MAC layer can also insert the so-called MAC control elements into the transport blocks to be transmitted over the transport channels. A MAC control element is used for inband control signaling—for example, timing-advance commands and random-access response. Control elements are identified with reserved values in the LCID field, where the LCID value indicates the type of control information.

Furthermore, the length field in the sub-header is removed for control elements with a fixed length.

Generally, one UE has a radio bearer comprising one PDCP entity, one RLC entity and one MAC entity. The MAC entity is performed for a base station with which the radio bearer is connected. However, there are cases that one UE has two different MAC entities sometimes (i.e. Dual Connectivity, Pro-Se, etc.).

FIG. 7 is a diagram for signaling of buffer status and power-headroom reports.

The scheduler needs knowledge about the amount of data awaiting transmission from the terminals to assign the proper amount of uplink resources. Obviously, there is no need to provide uplink resources to a terminal with no data to transmit as this would only result in the terminal performing padding to fill up the granted resources. Hence, as a minimum, the scheduler needs to know whether the terminal has data to transmit and should be given a grant. This is known as a scheduling request.

The use of a single bit for the scheduling request is motivated by the desire to keep the uplink overhead small, as a multi-bit scheduling request would come at a higher cost. A consequence of the single bit scheduling request is the limited knowledge at the eNodeB about the buffer situation at the terminal when receiving such a request. Different scheduler implementations handle this differently. One possibility is to assign a small amount of resources to ensure that the terminal can exploit them efficiently without becoming power limited. Once the terminal has started to transmit on the UL-SCH, more detailed information about the buffer status and power headroom can be provided through the inband MAC control message, as discussed below.

Terminals that already have a valid grant obviously do not need to request uplink resources. However, to allow the scheduler to determine the amount of resources to grant to each terminal in future subframes, information about the buffer situation and the power availability is useful, as discussed above. This information is provided to the scheduler as part of the uplink transmission through MAC control element. The LCID field in one of the MAC subheaders is set to a reserved value indicating the presence of a buffer status report, as illustrated in FIG. 7.

From a scheduling perspective, buffer information for each logical channel is beneficial, although this could result in a significant overhead. Logical channels are therefore grouped into logical-channel groups and the reporting is done per group. The buffer-size field in a buffer-status report indicates the amount of data awaiting transmission across all logical channels in a logical-channel group. A buffer status report represents one or all four logical-channel groups and can be triggered for the following reasons:

i) Arrival of data with higher priority than currently in the transmission buffer—that is, data in a logical-channel group with higher priority than the one currently being transmitted—as this may impact the scheduling decision.

ii) Change of serving cell, in which case a buffer-status report is useful to provide the new serving cell with information about the situation in the terminal.

iii) Periodically as controlled by a timer.

iv) Instead of padding. If the amount of padding required to match the scheduled transport block size is larger than a buffer-status report, a buffer-status report is inserted. Clearly it is better to exploit the available payload for useful scheduling information instead of padding if possible.

FIG. 8 is a diagram for short BSR MAC CE, and FIG. 9 is a diagram for long BSR MAC CE.

The Buffer Status Reporting (BSR) procedure is used to provide a serving eNB with information about the amount of data available for transmission (DAT) in the UL buffers of the UE. RRC may control BSR reporting by configuring the two timers periodicBSR-Timer and retxBSR-Timer and by, for each logical channel, optionally signalling Logical Channel Group which allocates the logical channel to an LCG (Logical Channel Group).

For the Buffer Status reporting procedure, the UE may consider all radio bearers which are not suspended and may consider radio bearers which are suspended. A Buffer Status Report (BSR) may be triggered if any of the following events occur:

-   -   UL data, for a logical channel which belongs to a LCG, becomes         available for transmission in the RLC entity or in the PDCP         entity and either the data belongs to a logical channel with         higher priority than the priorities of the logical channels         which belong to any LCG and for which data is already available         for transmission, or there is no data available for transmission         for any of the logical channels which belong to a LCG, in which         case the BSR is referred below to as “Regular BSR”;     -   UL resources are allocated and number of padding bits is equal         to or larger than the size of the Buffer Status Report MAC         control element plus its subheader, in which case the BSR is         referred below to as “Padding BSR”;     -   retxBSR-Timer expires and the UE has data available for         transmission for any of the logical channels which belong to a         LCG, in which case the BSR is referred below to as “Regular         BSR”;     -   periodicBSR-Timer expires, in which case the BSR is referred         below to as “Periodic BSR”.

A MAC PDU may contain at most one MAC BSR control element, even when multiple events trigger a BSR by the time a BSR can be transmitted in which case the Regular BSR and the Periodic BSR shall have precedence over the padding BSR.

The UE may restart retxBSR-Timer upon indication of a grant for transmission of new data on any UL-SCH.

All triggered BSRs may be cancelled in case UL grants in this subframe can accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its subheader. All triggered BSRs shall be cancelled when a BSR is included in a MAC PDU for transmission.

The UE shall transmit at most one Regular/Periodic BSR in a TTI. If the UE is requested to transmit multiple MAC PDUs in a TTI, it may include a padding BSR in any of the MAC PDUs which do not contain a Regular/Periodic BSR.

All BSRs transmitted in a TTI always reflect the buffer status after all MAC PDUs have been built for this TTI. Each LCG shall report at the most one buffer status value per TTI and this value shall be reported in all BSRs reporting buffer status for this LCG.

Buffer Status Report (BSR) MAC control elements consist of either: i) Short BSR and Truncated BSR format: one LCG ID field and one corresponding Buffer Size field (FIG. 8) or ii) Long BSR format: four Buffer Size fields, corresponding to LCG IDs #0 through #3 (FIG. 9).

The BSR formats are identified by MAC PDU subheaders with LCIDs as specified in Table 1.

TABLE 1 Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-10110 Reserved 10111 ProSe Truncated BSR 11000 Pro Se BSR 11001 Extended Power Headroom Report 11010 Power Headroom Report 11011 C-RNTI 11100 Truncated BSR 11101 Short BSR 11110 Long BSR 11111 Padding

The fields LCG ID and Buffer Size are defined as follow:

-   -   LCG ID: The Logical Channel Group ID field identifies the group         of logical channel(s) which buffer status is being reported. The         length of the field is 2 bits;     -   Buffer Size: The Buffer Size field identifies the total amount         of data available across all logical channels of a logical         channel group after all MAC PDUs for the TTI have been built.         The amount of data is indicated in number of bytes. It shall         include all data that is available for transmission in the RLC         layer and in the PDCP layer; the definition of what data shall         be considered as available for transmission. The size of the RLC         and MAC headers are not considered in the buffer size         computation. The length of this field is 6 bits. If         extendedBSR-Sizes is not configured, the values taken by the         Buffer Size field are shown in Table 2. If extendedBSR-Sizes is         configured, the values taken by the Buffer Size field are shown         in Table 3.

TABLE 2 Index Buffer Size (BS) value [bytes] 0       BS = 0 1      0 < BS <= 10 2     10 < BS <= 12 3     12 < BS <= 14 4     14 < BS <= 17 5     17 < BS <= 19 6     19 < BS <= 22 7     22 < BS <= 26 8     26 < BS <= 31 9     31 < BS <= 36 10     36 < BS <= 42 11     42 < BS <= 49 12     49 < BS <= 57 13     57 < BS <= 67 14     67 < BS <= 78 15     78 < BS <= 91 16     91 < BS <= 107 17    107 < BS <= 125 18    125 < BS <= 146 19    146 < BS <= 171 20    171 < BS <= 200 21    200 < BS <= 234 22    234 < BS <= 274 23    274 < BS <= 321 24    321 < BS <= 376 25    376 < BS <= 440 26    440 < BS <= 515 27    515 < BS <= 603 28    603 < BS <= 706 29    706 < BS <= 826 30    826 < BS <= 967 31    967 < BS <= 1132 32   1132 < BS <= 1326 33   1326 < BS <= 1552 34   1552 < BS <= 1817 35   1817 < BS <= 2127 36   2127 < BS <= 2490 37   2490 < BS <= 2915 38   2915 < BS <= 3413 39   3413 < BS <= 3995 40   3995 < BS <= 4677 41   4677 < BS <= 5476 42   5476 < BS <= 6411 43   6411 < BS <= 7505 44   7505 < BS <= 8787 45   8787 < BS <= 10287 46  10287 < BS <= 12043 47  12043 < BS <= 14099 48  14099 < BS <= 16507 49  16507 < BS <= 19325 50  19325 < BS <= 22624 51  22624 < BS <= 26487 52  26487 < BS <= 31009 53  31009 < BS <= 36304 54  36304 < BS <= 42502 55  42502 < BS <= 49759 56  49759 < BS <= 58255 57  58255 < BS <= 68201 58  68201 < BS <= 79846 59  79846 < BS <= 93479 60  93479 < BS <= 109439 61 109439 < BS <= 128125 62 128125 < BS <= 150000 63   BS > 150000

TABLE 3 Index Buffer Size (BS) value [bytes] 0       BS = 0 1       0 < BS <= 10 2      10 < BS <= 13 3      13 < BS <= 16 4      16 < BS <= 19 5      19 < BS <= 23 6      23 < BS <= 29 7      29 < BS <= 35 8      35 < BS <= 43 9      43 < BS <= 53 10      53 < BS <= 65 11      65 < BS <= 80 12      80 < BS <= 98 13      98 < BS <= 120 14     120 < BS <= 147 15     147 < BS <= 181 16     181 < BS <= 223 17     223 < BS <= 274 18     274 < BS <= 337 19     337 < BS <= 414 20     414 < BS <= 509 21     509 < BS <= 625 22     625 < BS <= 769 23     769 < BS <= 945 24     945 < BS <= 1162 25    1162 < BS <= 1429 26    1429 < BS <= 1757 27    1757 < BS <= 2161 28    2161 < BS <= 2657 29    2657 < BS <= 3267 30    3267 < BS <= 4017 31    4017 < BS <= 4940 32    4940 < BS <= 6074 33    6074 < BS <= 7469 34    7469 < BS <= 9185 35    9185 < BS <= 11294 36   11294 < BS <= 13888 37   13888 < BS <= 17077 38   17077 < BS <= 20999 39   20999 < BS <= 25822 40   25822 < BS <= 31752 41   31752 < BS <= 39045 42   39045 < BS <= 48012 43   48012 < BS <= 59039 44   59039 < BS <= 72598 45   72598 < BS <= 89272 46   89272 < BS <= 109774 47  109774 < BS <= 134986 48  134986 < BS <= 165989 49  165989 < BS <= 204111 50  204111 < BS <= 250990 51  250990 < BS <= 308634 52  308634 < BS <= 379519 53  379519 < BS <= 466683 54  466683 < BS <= 573866 55  573866 < BS <= 705666 56  705666 < BS <= 867737 57  867737 < BS <= 1067031 58  1067031 < BS <= 1312097 59  1312097 < BS <= 1613447 60  1613447 < BS <= 1984009 61  1984009 < BS <= 2439678 62  2439678 < BS <= 3000000 63    BS > 3000000

If a UE is connected to one eNB, the eNB is responsible for scheduling of the UE. Therefore, the UE reports its buffer status to the eNB in order to request the uplink resource. In Dual Connectivity, the UE can be scheduled by two eNBs. Therefore, the UE reports its buffer status to both eNBs as duplicated. As the UE reports its buffer status to all eNBs, e.g., when the amount of PDCP data is equal to or larger than a threshold, the UE is provided uplink resource from all eNBs which would be larger than the amount of data in the buffer. Accordingly, it is inevitable to avoid waste of uplink resource.

However, one assumption in allowing duplicated BSR towards all eNBs was that waste of resource may happen at the end of data burst and/or both eNBs may coordinate each other via network implementation.

In New RAT, the UE may be scheduled by multiple scheduling nodes, e.g., Distributed Units (DU), which would schedule the UE by considering radio condition between the UE and the scheduling node. Applying the same rule of DC to NR, the UE would report its buffer size to all scheduling nodes. Then, duplicated BSR operation would lead to a significant waste of uplink resources. Furthermore, it may be more complicated and not easy to coordinate/negotiate between all those scheduling nodes.

FIG. 10 is an exemplary diagram illustrating legacy BSR operation in multiple connectivity. Referring to FIG. 10, a UE may have a plurality of lower entities (e.g. lower entity 1 to lower entity 4) connected to a upper entity, and each lower entity may receive information on a buffer size from an upper entity. Then, each lower entity adds the buffer size of the upper entity received together with its buffer size (e.g. Buffer Size 1=Buffer Size of upper entity+Buffer Size of lower entity 1), and transmits the BSR to each scheduling node. In this case, as mentioned above, duplicated BSRs may be transmitted, which may result in waste of uplink resources. Therefore, a new mechanism is needed to report the UE's buffer size to only a part of scheduling nodes.

In the present invention, the following can be assumed.

-   -   Multiple-split bearer is a radio bearer that can be scheduled by         multiple scheduling nodes, e.g., three scheduling nodes.     -   A multiple-split bearer comprises one upper entity and multiple         lower entities, each of which has its own buffer for that         bearer.     -   Upper entity refers, e.g. packet data convergence protocol         (PDCP), while lower entity refers, e.g., Radio Link Control         (RLC) or medium access control (MAC).     -   In New RAT, the lower entity may include/perform BSR         functionality, which is located in MAC entity in LTE.     -   In LTE, the upper entity buffer refers PDCP buffer and the lower         entity buffer refers RLC buffer, while the BSR functionality is         performed in MAC entity, which is also called as lower entity in         this invention.     -   Each lower entity corresponds to one eNB.

The present invention may be applied to LTE dual connectivity, LTE WLAN aggregation, LTE-New RAT Integration, and Any technology using aggregation in LTE or New RAT.

FIG. 11 is a flowchart according to an embodiment of the present invention.

In transmitting the buffer status report (BSR) by the UE, the MAC entity may trigger the BSR (S1110). Subsequently, the UE may transmit the buffer state report (S1120). In this example, when a multiple-split bearer is configured to a UE, the lower entity of the radio bearer (RB) may report an amount of data available for transmission in lower entity, i.e., lower entity buffer size (LBS) information, to the eNB. In addition, when the lower entity reports the LBS to the eNB, if upper entity buffer size (UBS) reporting condition is met, the lower entity may report another amount of data available for transmission in upper entity, i.e., upper entity buffer size (UBS) information, to the eNB. The UBS reporting condition can be represented by the PDCP BSR condition. In addition, the upper entity buffer size (UBS) can be represented by the PDCP buffer size. At this time, the LBS information and UBS information may be transmitted via a separate signal. At this, upper entity buffer size (UBS) refers an amount of data available for transmission in upper entity, and lower entity buffer size (LBS) refers an amount of data available for transmission in lower entity.

If the UE is configured with a multiple-split bearer, the lower entity of the RB may report the buffer size of lower entity by using a lower entity buffer status report (LBSR) signal. When a multiple-split bearer is configured to a UE, the UE may receive a radio bearer (RB) configuration including information related to UBS reporting condition, which is used for the lower entity to decide whether UBSR is reported together with LBSR. For example, UBS reporting condition may be lower entity identifiers, UBS threshold, or periodicity, etc. The lower entity may report UBS by using an upper entity buffer status report (UBSR) signal separated from LBSR signal.

As an example, the UBS reporting condition may be at least one of the following:

(i) Whenever the LBSR signal is generated and/or transmitted by any lower entities of the RB.

(ii) When the LBSR signal is generated and/or transmitted by a specific lower entity of the RB. The specific lower entity of the RB is indicated by a lower entity identifier in the RB configuration.

(iii) When the UBS is equal to or larger than a specific value. The specific value is indicated by a UBS threshold in RB the configuration.

(iv) When a lower entity of the RB generates and/or transmits certain number of the LBSR signal. The certain number is indicated by a periodicity in RB the configuration.

(v) When a certain time has passed since the last generated and/or transmitted LBSR signal by a lower entity of the RB. The certain time is indicated by a periodicity in RB the configuration.

(vi) Any combination of above conditions. For example, when the LBSR signal is generated and/or transmitted by a specific lower entity of the RB and the UBS is equal to or larger than a specific value.

If the UE receives a RB configuration when configuring a multiple-split bearer, in BSR operation, the upper entity of the RB may indicate the UBS to the lower entity of the RB. After then, the lower entity of the RB may calculate the LBS for the RB and generates a LBSR signal and the lower entity checks whether UBS reporting condition is met or not. If UBS reporting condition is met, the lower entity of RB may generate a UBSR signal by setting the buffer size as indicated by upper entity, i.e., UBS. On the other hand, if UBS reporting condition is not met, the lower entity of RB doesn't generate the UBSR signal.

Alternatively, the upper entity of the RB may indicate the UBS to the lower entities of the RB only if the UBS is equal to or larger than the UBS threshold. Otherwise, the upper entity of the RB may indicate the UBS as zero to the lower entities of the RB.

If the lower entity of the RB generates a LBSR signal, the lower entity may transmit the generated LBSR signal to the corresponding eNB. If the lower entity of the RB also generates a UBSR signal, the lower entity may transmit the generated UBSR signal together with the LBSR signal. The lower entity of the RB may transmit the LBSR signal and the UBSR signal in the same PDU.

The LBSR signal may include LBS field indicating LBS, and UBSR signal includes UBS field indicating UBS. The LBSR signal and the UBSR signal may be identified by a specific identifier, e.g., LCID in LTE.

FIG. 12 is a block diagram of a communication apparatus according to an embodiment of the present invention.

The apparatus shown in FIG. 12 can be a user equipment (UE) and/or eNB adapted to perform the above mechanism, but it can be any apparatus for performing the same operation.

As shown in FIG. 12, the apparatus may comprise a DSP/microprocessor (110) and RF module (transceiver; 135). The DSP/microprocessor (110) is electrically connected with the transceiver (135) and controls it. The apparatus may further include power management module (105), battery (155), display (115), keypad (120), SIM card (125), memory device (130), speaker (145) and input device (150), based on its implementation and designer's choice.

Specifically, FIG. 12 may represent a UE comprising a receiver (135) configured to receive a request message from a network, and a transmitter (135) configured to transmit the transmission or reception timing information to the network. These receiver and the transmitter can constitute the transceiver (135). The UE further comprises a processor (110) connected to the transceiver (135: receiver and transmitter).

Also, FIG. 12 may represent a network apparatus comprising a transmitter (135) configured to transmit a request message to a UE and a receiver (135) configured to receive the transmission or reception timing information from the UE. These transmitter and receiver may constitute the transceiver (135). The network further comprises a processor (110) connected to the transmitter and the receiver. The processor (110) is configured to perform operations according to the embodiment of the present invention exemplarily described with reference to the accompanying drawings. In particular, the detailed operations of the processor (110) can refer to the contents described with reference to FIGS. 1 to 11.

The embodiments of the present invention described herein below are combinations of elements and features of the present invention. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present invention may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present invention may be rearranged. Some constructions of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions of another embodiment. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present invention or included as a new claim by subsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operation described as performed by the BS may be performed by an upper node of the BS. Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with an MS may be performed by the BS, or network nodes other than the BS. The term ‘eNB’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, for example, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments of the present invention may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to the embodiments of the present invention may be implemented in the form of modules, procedures, functions, etc. performing the above-described functions or operations. Software code may be stored in a memory unit and executed by a processor. The memory unit may be located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present invention may be carried out in other specific ways than those set forth herein without departing from essential characteristics of the present invention. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the invention should be determined by the appended claims, not by the above description, and all changes coming within the meaning of the appended claims are intended to be embraced therein. 

What is claimed is:
 1. A method for transmitting, by a user equipment (UE), a buffer status report in a wireless communication system, the method comprising: triggering, by a medium access control (MAC) entity, a buffer status report (BSR); and transmitting the buffer status report, wherein the buffer status report includes a packet data convergence protocol (PDCP) buffer size for a radio bearer only if PDCP BSR condition is met.
 2. The method of claim 1, wherein the buffer status report includes a first value for the PDCP buffer size if the PDCP BSR condition is met and a second value for a radio link control (RLC) buffer size.
 3. The method of claim 1, wherein the MAC entity is a MAC entity configured to transmit the PDCP buffer size.
 4. The method of claim 1, wherein the PDCP BSR condition is at least one of: when the PDCP buffer size is equal to or larger than a threshold, when a certain number of BSRs without the PDCP buffer size is generated by the MAC entity, or when a certain time has passed since a last BSR without PDCP buffer size is generated by the MAC entity.
 5. The method of claim 1, wherein the radio bearer comprises one PDCP entity and multiple RLC entities.
 6. A user equipment (UE) in a wireless communication system, the UE comprising: a radio frequency (RF) module configured to transmit/receive signals to/from a network; and a processor configured to process the signals, wherein the processor is configured to: trigger, by a medium access control (MAC) entity, a buffer status report (BSR); and transmit the buffer status report, wherein the buffer status report includes a packet data convergence protocol (PDCP) buffer size for a radio bearer only if PDCP BSR condition is met.
 7. The UE of claim 6, wherein the buffer status report includes a first value for the PDCP buffer size if the PDCP BSR condition is met and a second value for a radio link control (RLC) buffer size.
 8. The UE of claim 6, wherein the MAC entity is a MAC entity configured to transmit the PDCP buffer size.
 9. The UE of claim 6, wherein the PDCP BSR condition is at least one of: when the PDCP buffer size is equal to or larger than a threshold, when a certain number of BSRs without the PDCP buffer size is generated by the MAC entity, or when a certain time has passed since a last BSR without PDCP buffer size is generated by the MAC entity.
 10. The UE of claim 6, wherein the radio bearer comprises one PDCP entity and multiple RLC entities. 